Heater and shunt mechanism for overload relays



June 3, 1952 R. P. BALLOU 2,598,878

HEATER AND SHUNT MECHANISM FOR OVERLOAD RELAYS Filed April 10. 1948 IN V EN TOR.

Patented June 3, 1952 STATES OFFICE;

HEATER snoN'r MECHANISM FOR OVERLOAD RELAYS Richard P.- Ballou, Hartford,- Conm, assignoi'. to Federal Electric Products company; Newark;

Jr; a corporation Application April 10, 1948, SerialNo. 20363 4 claims.

The present invention relates to heaters for the thermo responsive elements of overload relaysor other control devices and to the provision of such heaters with shunts whereby to control the rating of the heater for controlling the operationof the overload relay or other device.

In its more specific aspects, this invention relates to heaters for overload relays of the type used to protect electric motors against excessive currents, usually according to an inverse time current relationship. According to the present invention, and pursuant to one of the objects thereof, the relay heater is provided with a shunt whereby a heater of fixed electrical and mechani= cal properties may have its heating characteristic increased without alteration of the relay itself. Thus for example, a comparatively small relay which may be composed of many intricate parts requiring expensive dies for the production thereof may have its current rating considerably increased without any change in the relay itself.

Another object of the invention is the provision or a relay heater and shunt combination of such character that the heat generated in the shunt has no appreciable heating effect on the thermorespensive element or the relay.

A further object of the invention is the provisionoi a heater which may be readily attached to the overload relay in accurate position and alignment in relation to the thermo-responsive element of the relay and to the points or attachment of electric terminals for the heater.

The above and other objects, features and advantages of the present invention will be fully understood from the following description considefed in connection with the accompanying illustrative drawing.

In the drawing:

Fig. 1 is a perspective View of an overload relay provided With a heater with a shunt eiiib'OdY- ins the present invention;

Fig; 2 end view of the combination shown in Fig. 1, a part or the casing of the relay bein cut away for the purpose of illustration;

Fig. 3 is a perspective view or the heater detalid from the relay and with the shunt removed, illustrating the heater in relation to the theiriio responsive element of the relay;

Fig. 4" is a perspective view of a heater with an integral shunt;

Figs. 5A and 5B are perspective views of two of different current ratings, respectively.

Referring now to the drawing in detail, the present invention is shown as applied to an over lead relay it of the construction shown by U. S.

Patent No. 2,343186-2', granted March 14; 1944 to Paul Christensen, but it will be understood that the invention is not limited to relays of that particular construction. The thermcnresponsive e1ement of saidrelay comprises the bi-' metallic strip indicated at i2 in Figs. 2 and 3.

The heater device M, which is formed in one piecefrom suitable metal includes the part It which constitutes the heater for the relay. Said heater device l4 includes attaching means here shown as ears l8 provided with o enings 20 for screws 22 by which said heater device is secured to the insulation casing 24 of the overload relay. As shown, casing 24 is provided with an opening 26 to receive the heater part I6, and it will be understood that said part is automatically disposed in proper relation to the thermo' sensitive element I2 of the relay when device M is secured in position by said screws 22. Th heater includes laterally spaced parts 28 and part It is bent therefrom so as to lie in a plane transversely of said spaced parts. The laterally spaced parts 28' of device [4 are provided with openings 30 for mounting device I4 on supporting means constitutedby metal lugs 32 which, as here shown, are in the form of screw-threaded rods in screwthreaded engagement with companion internally screw-threaded sleeves or studs 3 1. Lugs 32 project beyond both ends of the companion studs 3'4, and one end of each lug projects through an opening in the insulation panel P for connection to an electric terminal 36' which is disposed between a washer 38 and a clamping nut 40. Holes 30 of device M are considerably larger in diameter than lugs 32 thus obviatin the necessity for precise location of the relay In With respect to these lugs. Further in this connection it will be noted that the large size of holes 30 in relation to lugs 32 prevents distortion of the heater device in attachin it to the studs and thus obviates any modification of the characteristics of the relay and heater combination. Device i4 is secured to lugs 32 by nuts 42.

The shunt for the heater is in the form or a metal member or part here shown as a strip id of pre -determined thickness, said shunt being electrically and mechanically secured to lugs 32 and thus electrically connected between spaced parts 28- at points remote from heater part It,

said shun-t being remotely spaced also from the merino-element 12' whereby heat generated in the shunt will have substantially no heating effecton said element. Said shunt is provided with holes 46' through which the upper ends of the lugs 32 project, and nuts 48' are provided for securing the shunt in position in parallel circuit relation with heater part [6. In Figs. 5A and 53 two shunts 44 of different thicknesses, respectively, are shown, but it will be understood that a series of shunts of different thickness may be provided, so that a shunt of the desired thickness, according to the desired calibration of the relay, may be selected and applied in conjunction with the heater device l4 according to load protection requirements.

As illustrated in Fig. 4, the shunt may be formed integrally with the heater device. Otherwise, in this form of the invention the heater device MA may be of the same construction as the heater device [4 and is secured to the relay and to the lugs 32 in the same way as heater device I4. Accordingly it will be noted that the parts of heater device 14A which correspond to the similar parts of device l4 are designated by the same reference numerals with the added reference letter A. The shunt part or member MA, however, instead of varying in thickness as in the case of shunt 44 is of varying width as indicated by the dot-and-dash line L, in order to predetermine the current rating of the heater portion IGA for the thermo-responsive element IQ of the relay. As a result of this construction of unit MA, the shunt 44A can be made of the desired width by supplying sheet metal stock of proper width to the die that stamps out the part, or by an auxiliary shearing operation as indicated by the dot-and-dash line L. Thus units of different ratings may be made by the same die.

It will be observed that in the form of the invention illustrated in Figs. 1 to 3, as well as in the form of the invention illustrated in Fig. 4 the mounting ears I8 are spaced from the main body of the heater device and are of restricted width for the purpose of reducing the flow of heat into the relay by thermal conduction.

It will be noted that the relay it is provided with terminal members 50 to which the ears It (or 18A) of the heater device are secured by the fastening screws 22. Said terminal members are provided with terminal screws 52 by which the electric wires may be connected to the heater when the relay is provided with a heater of the form shown in the above mentioned Patent No. 2,343,862. In other words, it will be understood that a relay such as that shown by said patent may be supplied as the manufacturers standard form of relay, and that when it is desired to change the characteristics of the relay and heater combination, the heater supplied with the stand ard overload relay may be removed and replaced by the heater of the present invention. Thus, when the relay is furnished without the heater of the present invention, the mounting lugs and studs 32, 34 are not required and the wires for conducting the current through the heater instead of being connected to the lugs 32 are connected to the terminals 50 by screws 52 and the heater supplied with the standard overload relay is connected to said terminals 50 by the screws 22.

It will be understood that the present invention may be embodied in various specific constructions other than those herein illustrated or specifically described and that various changes in the details of construction and in the arrangement of parts may be made without departing from the underlying idea or principles of my invention within the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. An electric heater for a thermostatic control device of an automatic circuit breaker, comprising an electrically conductive heater member having a heater part adjacent one end thereof, laterally spaced terminal portions in electrically conductive relation to said heater part for connecting said member in an electric circuit, said laterally spaced terminal portions being spaced from said heater part whereby the latter may be mounted adjacent to said thermostatic control device and is thermally remote from said terminal portions so that when the latter are bridged by a shunt the heat generated by the current traversing said shunt is substantially prevented from heating said heater part, and portions disposed adjacent said end of the heater member for mounting the latter on the circuit breaker.

2. An electric heater for a thermostatic control device of an automatic circuit breaker, comprising an electrically conductive heater member having a heater part adjacent one end thereof, laterally spaced terminal portions in electrically conductive relation to said heater part for connecting said member in an electric circuit, said laterally spaced terminal portions being spaced from said heater part whereby the latter may be mounted adjacent to said thermostatic control device and is thermally remote from said terminal portions so that when the latter are bridged by a shunt the heat generated by the current traversing said shunt is substantially prevented from heating said heater part, said heater part and said terminal portions being formed in one piece of sheet metal and being disposed, respectively, in planes transversely of each other.

3. An electric heater for a thermostatic control device of an automatic circuit breaker, comprising an electrically conductive heater member having a heater part adjacent one end thereof, laterally spaced terminal portions in electrically conductive relation to said heater part for connecting said member in an electric circuit, said laterally spaced terminal portions being spaced from said heater part whereby the latter may be mounted adjacent to said thermostatic control device and is thermally remote from said terminal portions so that when the latter are bridged by a shunt the heat generated by the current traversing said shunt is substantially prevented from heating said heater part, a support provided wih spaced terminal lugs, said spaced portions having apertures to receive said lugs, said apertures being larger than said lugs for clearance therebetween, and means for fastening said spaced portions to said lugs.

4. An electric heater for a thermostatic control device of an automatic circuit breaker, comprising an electrically conductive heater member having a heater part adjacent one end thereof, laterally spaced terminal portions in electrically conductive relation to said heater part for'connecting said member in an electric circuit, said laterally spaced terminal portions being spaced from said heater part whereby the latter may be mounted adjacent to said thermostatic control device and is thermally remote from said terminal portions so that when the latter are bridged by a shunt the heat generated by the current traversing said shunt is substantially prevented from heating said heater part, a support provided with spaced terminal lugs, said spaced portions having apertures to receive said lugs, said apertures being larger than said lugs for clearance therebetween, means for fastening-said spaced portions to said lugs, and a shunt adapted to be electrically connected to said lugs and to said spaced terminal portions whereby the current supplied to said terminal lugs on said support is fed to said heater part and to said shunt in parallel circuit relation.

RICHARD P. BALLOU.

REFERENCES CITED The following references are of record in the file of this patent:

Number 6 UNITED STATES PATENTS Name Date Hoyt Dec. 10, 1912 Campbell Nov. 22, 1927 Schnetzler July 30, 1929 Chapman Apr. 25, 1933 Lederer Mar. 20, 1934 Trombetta Feb. 26, 1935 Frese June 16, 1936 Christensen Mar. 14, 1944 Van Hoorn June 17, 1947 Anderson Apr. 6, 194:? 

